Sealed belt tensioning device

ABSTRACT

A tensioning system including a base and an arm pivotally coupled to the base, the arm having an engagement surface and being configured to pivot relative to the base about a pivot axis. The system further includes a biasing mechanism operatively coupled to the arm to bias the arm relative to the base, and a seal assembly sealingly positioned between the arm and the base. The seal assembly is coaxial with the pivot axis and configured to accommodate relative axial movement between the base and the arm and relative radial movement between the base and the arm while still maintaining a seal therebetween.

The present invention is directed to a belt tensioning device, and moreparticularly, to a belt tensioning device with one or more sealsincorporated therein.

BACKGROUND

Belt tensioners are utilized to ensure the associated belt, such as abelt in an automotive vehicle, is placed and maintained in the desiredstate of tension. Such belt tensioners can in some cases be exposed toenvironmental factors and outside contaminants, such as dust, dirt,fluids, etc. However, many existing belt tensioners do not providesufficient protection from such environmental factors and outsidecontaminants.

SUMMARY

In one embodiment, the present invention is belt tensioning deviceincorporating one or more seals to protect the belt tensioning devicefrom environmental factors and outside contaminants. More particularly,in one embodiment the invention is a tensioning system including a baseand an arm pivotally coupled to the base, the arm having an engagementsurface and being configured to pivot relative to the base about a pivotaxis. The system further includes a biasing mechanism operativelycoupled to the arm to bias the arm relative to the base, and a sealassembly sealingly positioned between the arm and the base. The sealassembly is coaxial with the pivot axis and configured to accommodaterelative axial movement between the base and the arm and relative radialmovement between the base and the arm while still maintaining a sealtherebetween.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a front view of a belt system utilizing a tensioner;

FIG. 2 is a side cross section of the tensioner of FIG. 1, taken alongline 2-2;

FIG. 3 is a side cross section of an alternate tensioner;

FIG. 3A illustrates an O-ring seal in cross section;

FIG. 3B illustrates an X-ring seal in cross section;

FIG. 3C illustrates a U-ring seal in cross section.

FIG. 4 is a side cross section of another alternate tensioner; and

FIG. 5 is a side cross section of yet another alternate tensioner.

DETAILED DESCRIPTION

FIG. 1 is a front view of a belt system, generally designed 10, shown inassociation with a belt tensioner 12. The belt system 10 includes anendless power transmitting element 14, such as a belt, chain or thelike, which passes around a variety of pulleys, gears, guides. The powertransmitting element 14 thereby drives a plurality of drivenaccessories, and/or is driven by one or more of the components. Thepower transmitting element 14 can, in one case, take the form of atiming belt/chain, a drive belt/chain, a transmission belt/chain or thelike for use in an automotive vehicle. The tensioner 12 engages thepower transmitting element 14 to apply the desired force to the powertransmitting element 14 and to induce the desired tension.

With reference to FIGS. 1 and 2, the tensioner 12 includes an arm 18movably coupled to a spring case or base 20. The tensioner 12 furtherincludes a belt engagement surface 22 positioned at one end of the arm18, and a biasing mechanism or energy storing device 24 positionedbetween and operatively engaging the arm 18 and spring case 20. In oneembodiment, the belt engagement surface 22 takes the form of a generallycylindrical roller 26 rotatably coupled to the arm 18 via a bearing 28,as shown in FIG. 2, such that the roller 26 can rotate as the belt 14rolls past the tensioner 12. Alternately the belt engagement surface 22can take the form of a smooth, but non-rotatable, component withhigh-lubricity, or a toothed sprocket (for use with a chain), etc. Thebelt engagement surface 22 is aligned with, and/or rotatable about, anaxis 31.

The arm 18 is pivotally coupled to the spring case 20, and the springcase 20 is configured to be fixedly and non-rotatably coupled to ananchor body 30, such as an engine, engine block, engine cover, frame,etc. In one embodiment the tensioner 12/spring case 20 is coupled to theanchor body 30 by a threaded fastener 32, such as a bolt, extendingthrough a central opening 34 of a pivot tube 37 of the tensioner 12 andinto the anchor body 30. The bolt 32 thereby defines, or is alignedwith, an axis 33 about which the arm 18 is pivotable. The axis 33 isthus, in the illustrated embodiment, radially offset from the axis 31 ofthe belt engagement surface 22. The tensioner 12 could also beconfigured in and/or mounted in various other configurations andmanners, such as in a tab/ear mounting configuration.

The biasing mechanism 24 can take the form of a spring, such as ahelical coil spring in the illustrated embodiment. The biasing mechanism24 urges the arm 18/roller 26 into contact with the belt 14 with thedesired amount of force, and allows the arm 18 to pivot about the axis33 (i.e. in the directions of the arrow 36 shown in FIG. 1) toaccommodate varying forces applied to the arm 18/roller 26 by the belt14. A bushing 40 is positioned between the arm 18 and the spring case20, and a spring cap 42, or cover, is located at one axial end of thespring 24 to cover and protect the spring 24.

In the embodiment of FIG. 2, the arm 18 includes a pulley portion 18 acarrying the roller 26 and a body portion 18 b positioned adjacent tothe spring case 20. The body portion 18 b of the arm 18 includes agenerally flat, center annular portion 44, a radially outer flange 46,and a radially inner flange 48 positioned between the center portion 44and the outer flange 46 in the radial direction. The arm 18 alsoincludes a connecting portion 50 positioned between the outer 46 andinner 48 flanges. The spring 24 is positioned adjacent to and radiallyinside the radially inner flange 48, and above and adjacent to thecenter portion 44.

The spring case 20 includes an inner cylindrical portion 52, an outercylindrical portion 56 and a generally flat body portion 54 positionedbetween the inner cylindrical portion 52 and the outer cylindricalportion 56 in the radial direction. The outer cylindrical portion 56includes an end flange 58 extending radially outwardly from an upper endthereof. The outer cylindrical portion 56 and the end flange 58 of thespring case 20 are positioned between the outer flange 46 and the innerflange 48 of the arm 18 in a radial direction thereof. In this mannervarious portions of the arm 18 and spring case 20 nest, or overlap, inthe axial and/or radial directions.

The spring cap 42 is positioned at the upper, central end of thetensioner 12. The spring cap 42 includes an inner tube portion 60 whichis positioned between the pivot tube 37 and the spring 24 such that thespring 24 is positioned between the inner tube portion 60/spring cap 42and the radially inner flange 48 of the arm 18 in the radial direction.

One end of the spring 24 is fixedly coupled to the arm 18 (e.g. in onecase to the radially inner flange 48, or connecting portion 50, orcenter portion 44 of the arm 18), and the other end of the spring 24 isfixedly coupled to the spring cap 42 (e.g. in one case to the inner tubeportion 60 of the spring cap 42). The spring cap 42 is, in turn, fixedlycoupled to the spring case 20 via the pivot tube 37. In this manner,when the arm 18 is pivoted (i.e. in the direction of arrows 36 of FIG.1), the spring 24 is wound or unwound, depending upon the direction ofpivoting, to provide the desired biasing force to the arm 18.

In the embodiment of FIG. 2, the bushing 40 is positioned between thearm 18 and the spring case 20. In the illustrated embodiment the bushing40 includes a cylindrical portion 62 at one end thereof, a flangeportion 64 at the other end thereof, and a generally conical portion 66positioned between the flange portion 64 and the cylindrical portion 62.The cylindrical portion, or pivot bushing 62, helps to provide properradial alignment between the arm 18 and spring case 20, and ispositioned between the outer cylindrical portion 56 of the spring case20 and the radially inner flange 48 of the arm 18. The flange portion ofthe bushing, or spring bushing 64, helps to provide proper axialalignment between the arm 18 and the spring case 20, and is positionedbetween the end flange 58 of the spring case 20 and the connectingportion 50 of the arm 18.

Finally, the conical portion of the bushing, or the damper bushing 66,provides damping characteristics to the tensioner 12, and can provideradial and/or axial positioning between the arm 18 and spring case 20,and is positioned between the outer cylindrical portion 56 of the springcase 20 and the radially inner flange 48 of the arm 18. The bushing 40can be made from a wide variety of materials, but is made of plastic orpolymer materials in one case. Further details relating to tensioners,which can utilize the seals disclosed herein, can be found in U.S. Pat.Nos. 7,497,796, 7,887,445, 8,075,433, and 6,575,860, the entire contentsof which are incorporated herein.

In some cases environmental factors and outside contaminants, such asdust, dirt, fluids, etc. can penetrate the tensioner 12 and cause thebushing 40, or other components, to wear. Wearing of the bushing 40 orother components can adversely effect the performance of the tensioner12. Therefore, in the embodiment of FIG. 2 a seal system 70 is providedto reduce the penetration of contaminants to the bushing or othercomponents.

The illustrated seal system 70 includes a V-ring seal 72, or lip seal,having a body portion 74 and an integral, flexible flange 76. A gap 78is positioned between the flange 76 and the body portion 74, and theflange 76 is relatively thin, and therefore deflectable, relative to thebody portion 74. In the illustrated embodiment, the seal 72 ispositioned on the radially outer surface of the outer cylindricalportion 56, and below the end flange 58 of the spring case 20.

The seal system 70 further includes a seal plate 80 that is coupled tothe outer flange 46 of the arm 18, extending radially inwardlytherefrom. The seal plate 80 can be secured to the outer flange 46/arm18 by staking, but could also be secured by various means, such aswelding, adhesives, brazing, etc. Alternatively, the seal plate 80 canbe formed as a unitary one-piece body with the arm 18/outer flange 46.

The upper surface 82 of the seal plate 80 defines a seal counterfacewhich sealingly engages the flange 76 of the seal 72. In particular, theseal 72 and seal plate 80 are arranged such that the seal 72/flange 76is placed into compression in the axial direction when the tensioner 12is assembled/mounted to ensure proper sealing and allow for wear in thetensioner 12. The seal 72 may also be stretched/placed in tension in theradial direction by stretching the seal 72 to a greater diameter thanthe seal 72 assumes when it is not mounted to the tensioner 12. The seal72 can be made of a wide variety of materials, such as rubber, syntheticrubber, a butyl material, a trial nitrile, etc. Moreover, the seal 72can take a variety of configurations besides the V-ring seal shownherein, such as O-rings (FIG. 3A), X-rings (FIG. 3B) and U-rings (FIG. 3C). The seal 72 may be relatively compressible but have the ability toaccommodate relatively high tolerances and wear. In particular, it maybe desired for the seal 72 to be compressible to allow sometravel/movement, but not provide much resistance to suchtravel/movement. The V-ring seal provides a relatively high amount oftravel (to allow for wear and tolerance) without much compressive force,thereby reducing temporary damping and damping variation from sealcontact. However, other shapes can be utilized.

As the flange portion 64 of the bushing 40 wears, the axial position ofthe arm 18 relative to the spring case 20 can be shifted (typically, thearm 18 and spring case 20 on either side of the flange portion 64 movecloser together in the axial direction). This shift in position causesthe seal plate 80 to move axially away from the seal 72. In this casethe seal 72/flange 76 simply expands in the axial direction, increasingits gland size, following the seal plate 80 and maintaining a properseal. On the other hand, if the seal plate 80 were to move toward theseal 72 (for example, due to uneven wear of the bushing 40 causingcanting or skewing of the arm 18 relative to the spring plate 20), theseal 72/flange 76 will be compressed, decreasing its gland size, andagain maintaining a proper seal.

Therefore, the seal assembly 70 can accommodate a shift in axialposition between the seal plate 80 and seal 72 in either axialdirection. In this manner wearing of the bushing 40, and axial shifts inposition between the arm 18 and spring case 20, are easily accommodated.

The seal assembly 70 can also accommodate wear in the cylindricalportion 62 of the bushing 40. In particular, such wear may cause theseal 72 to move radially inwardly or outwardly relative to the sealplate 80. In this case, however, the flange 76/seal 72 simply slidesradially inwardly across the seal plate 80/counterface 82 to accommodatesuch a shift in position. The seal assembly 70 may have or provideradial clearance for the seal 72 on either side of the seal plate 80 toallow the seal 72/flange 76 to slide radially across the seal plate 80,while maintaining the seal. However, it should be noted that such radialmovement of the seal 72 across the seal plate 80 is designed toaccommodate wear, and is not necessarily designed to accommodateoff-center or eccentric movement of the arm 18 relative to the springcase 20.

Wear of the conical portion 66 of the bushing 40 may cause the seal 72to shift both axially and radially relative to the seal plate 80. Asdescribed above, however, the compressible/movable nature of the seal 72enables the seal assembly 70 to accommodate such wear/movement. As alsonoted above, the bushing 40 or parts thereof may wear unevenly overtime, which can cause the arm 18 to pitch, or form an angle, relative tothe spring case 20. The flexible, dynamic nature of the seal assembly 70therefore allows the seal assembly 70 to accommodate such pitching oroffset of the arm 18.

The seal assembly 70 thereby maintains a seal around the bushing 40 toprevent contaminants, such as dust, dirt, fluids and other environmentalfactors from reaching the bushing 40, helping to ensure proper operationof the tensioner 12 and extending the life of the tensioner. Theillustrated seal assembly 70 is also positioned radially outside thespring 24, isolating the spring 24 from the outside environment. Theseal assembly 70 thus helps to protect the spring 24, extend its usefullife, and ensuring proper operation of the tensioner 12.

In the illustrated embodiment, the seal 72/seal assembly 70 isconcentrically/coaxially mounted relative to the bolt 32/axis 33. Thisarrangement helps to ensure that, under normal operating conditions, theseal 72 does not move in the radial direction relative to the sealcounterface 82 whenever the arm 18 is pivoted relative to the springcase 20. In particular, repeated radial movement of the seal 72 relativeto the seal counterface 82 could create a sweeping action that couldlead to the introduction of contaminants inside the seal assembly 70,which could cause wear in the bushing 40 or other components, and couldalso cause wear in the seal 72 itself.

FIG. 2 illustrates the seal 72 in a particular arrangement in which theflange 76 of the seal 72 is positioned on the bottom side of the seal72, engaging the seal plate 80. However, this configuration can bereversed such that the body 74 of the seal 72 is positioned adjacent tothe seal plate 80, and the flange 76 of the seal 72 is positioned at thetop, engaging the end flange 58 of the spring case 20. In this reversedconfiguration the seal assembly 70 can still accommodate axial andradial movement between the arm 18 and spring case 20 in all directions.Moreover, the seal 72 can be turned on its side in either directionthereof, such that the flange 76 faces either the outer cylindricalportion 56 of the spring case 20 or the radially outer flange 46 of thearm 18, while still maintaining a proper seal and accommodating relativeaxial and radial movements between the arm 18 and spring case 20. Thus,the seal 72 can be rotated 90°, 180°, or 270° from its position shown inFIG. 2.

FIG. 3 illustrates an alternate embodiment having a seal assembly 70′similar to that of FIG. 2 and described above. The tensioner 12 of FIG.3 is somewhat similar to that of FIG. 2, but utilizes a pivot tube 37formed as one piece with the spring case 20, and the spring 24 is anexpansion spring which unwinds as the tensioner 12 moves from its freearm to its nominal position. Moreover, the spring cap 42 has an innertube portion 60 with a shorter axial length than that in the embodimentof FIG. 2

In the embodiment of FIG. 3 the seal 72 is positioned above (instead ofbelow) the end flange 58 of the spring case 20, and engages theunderside of the connecting portion 50 of the arm 18. In this manner,the underside of the connecting portion 50 acts as the seal counterface82 that the seal 72 flexibly and sealingly engages, providing the samebenefits as described above in the embodiment of the FIG. 2. Moreover,the seal 72, in this embodiment, is rotated 180° from the position ofthe seal 72 shown in the embodiment of FIG. 2 such that the flange 76 ispositioned on the top side of the seal 72. The seal 72 in FIG. 3 (aswell as the other embodiments described below and shown in FIGS. 4 and5) can also be arranged in the various other configurations andorientations, and take the form of the various seals and utilize thesame materials described above in the context of FIG. 2.

Since the seal 72, in the embodiment of FIG. 3, is positioned on top ofthe end flange 58, instead of the below the end flange 58 (as in theembodiment of FIG. 2), the seal 72 will be compressed (instead ofexpand) when the arm 18 and spring case 20 move closer together (e.g.when the flange portion 64 of the bushing 40 wears). In this case,however, the seal 72/flange 76 is simply compressed and retains thedesired seal.

The embodiment of FIG. 3 also utilizes a supplemental, or secondary seal86. In this embodiment, the secondary seal is a V-ring seal 86 having abody portion 88, flange 90 and gap 92. The secondary seal 86 issealingly positioned between the spring cap 42 and the arm 18, in agroove 94 on the underside of the spring cap 42. In the illustratedembodiment, the secondary seal 86 is positioned adjacent to the head ofthe fastener 32 (e.g., in one case, closer to the head of the fastener32 than to the distal end). The secondary seal 86 of FIG. 3 can also belocated in any of the four rotational positions described above for theprimary seal.

The secondary seal 86 can have the same dynamic seal characteristics asthe primary seal 72 described above. For example, as the spring bushing40, or flange portion 64 of the bushing 40, wears, the axial gap betweenthe arm 18 and spring case 24 may be reduced, thereby causing the arm 18to move away from the spring cap 42, and the secondary seal 86 expands(i.e. its gland area increases). Thus, it can be seen that the primary72 and secondary 86 seals, in the embodiment of FIG. 3, operate intandem such that as one seal 72/86 expands, the other is compressed.However, it is also possible that the primary seal 72 can utilize theconfiguration/orientation shown in FIG. 2, in which case the primary 72and secondary 86 seals would expand/compress in the same manner.

The secondary seal 86 blocks external contaminants from reaching thebushing 40 through any gap between the spring cap 42 and the arm 18.Thus the primary seal 72 prevents contaminants from reaching a first(upper) exposed end of the bushing 40, and the secondary seal 86prevents contaminants from reaching a second (lower) exposed end of thebushing 40. The secondary seal 86 of FIG. 3 can also be utilized in thetensioner of FIG. 2, or in the other designs disclosed herein.

FIG. 4 illustrates another tensioner 12 which is somewhat similar inoperation and principle to those of FIGS. 2 and 3, but utilizes alower-offset design. Moreover, rather than having portions of the arm 18and spring case 20 nest or overlap significantly in the axial direction,the arm 18 and spring case 20 meet in a planar face-to-face contact areaseparated by a spring bushing or flange bushing 64. The inner flange 48of the arm 18 is positioned radially inside the spring 24, adjacent tothe pivot tube 37. The tensioner 12 of FIG. 4 further includes a pivotbushing 62 between the arm 18 and the pivot tube 37, and a damperbushing 66 positioned at an axial top surface thereof. A deflected armplate, or cover 98, is positioned on top of the damper bushing 66 tomaintain the damper bushing 66 in place. In this embodiment, then,rather than having a single bushing 40 with three separate portions toprovide three separate functions, three separate bushing 62, 64, 66 areprovided, each bushing 62, 64, 66 providing a separate function.

The embodiment of FIG. 4 uses a seal system 70″ which is similar inappearance and function to the seal system 70′ disclosed in FIG. 3. Inparticular, the seal 72 is positioned such that the body 74 ispositioned adjacent to (and above) the end flange 58 of the spring case20, and the flange 76 of the seal 72 engages the arm 18. However, in theembodiment of FIG. 4 the seal system 70″ is positioned atroughly/generally the axial midpoint of the tensioner 12 and positionedadjacent to the spring bushing 64 to fluidly isolate the spring bushing64 and prevent contaminants from contacting the spring bushing 64.

The embodiment of FIG. 4 also utilizes a secondary seal 86′, somewhatsimilar to the secondary seal 86 of FIG. 3. However, the secondary seal86′ of FIG. 4 is positioned between the arm 18 and the deflected armplate 98. Moreover, the secondary seal 86′ in FIG. 4 is shown rotated180° from the position of secondary seal 86 of FIG. 3. However, thesecondary seal 86′ of FIG. 4 can be located in either position. Thesecondary seal 86′ fluidly isolates and protects the damper bushing 66from contaminants.

In the embodiment of FIG. 4, when the spring bushing 64 wears, theprimary seal 72 will be further compressed (i.e. its gland area willdecrease). When the damper bushing 66 wears, the secondary seal 86′ willalso be further compressed (i.e. its gland area will decrease).

FIG. 5 illustrates another tensioner 12 with a moderate offset andutilizing a flat spring 24, instead of a spring with a round crosssection as in FIGS. 2-4. In this embodiment the pivot tube 37 is formedas one piece with the spring case 20. The tensioner of FIG. 5 12includes a bushing component 102 including both a cylindrical portion62, positioned between the arm 18 and the pivot tube 37/spring case 20,and a damper portion 66, positioned between the deflected arm plate 98and the arm 18. The tensioner 12 also includes a flange portion bushing64 positioned between the face-to-face contact area of the arm 18 andthe spring case 20, somewhat similar to the bushing 64 in the embodimentof FIG. 4.

In this embodiment, the seal 70′″ is positioned at a radially innerposition between the arm 18 and spring case 20, radially inside a sealstop 100 that is integral with the spring case 20. In this particularembodiment, the flat spring 24 includes an anchor hook which ispositioned externally of the spring case 20, thereby making sealing ofthe spring case 20/tenioner 12 difficult. Accordingly, in this case, theseal 70′″ is positioned radially inwardly of the spring 24, adjacent tothe bushing 62, and sealingly positioned between the arm 18 and springcase 20 to seal the bushing 62.

The secondary seal 86′ is positioned between the arm 18 and thedeflected arm plate 98, similar to the secondary seal 86′ in theembodiment of FIG. 4. However, in the embodiment of FIG. 5, thesecondary seal 86′ is positioned in a generally closed cavity andtherefore can be located in any of the four radial positions referencedabove. Thus, the primary 70′″ and secondary 86′ seals of FIG. 5 seal thecylindrical portion 62 and damper bushing portions 60 to ensure properoperation of the tensioner 12.

As can be seen, the various seals disclosed herein help to preventcontaminants from reaching various internal components of the tensioner,including in various cases the bushings or parts thereof, the spring, orother parts. Reducing the introduction of contaminants thereby helps toprovide longer life and proper operation to the tensioner, which in turnextends the life and ensure proper operation of the belt system 10.

Having described the invention in detail and by reference to certainembodiments, it will be apparent that modifications and variationsthereof are possible without departing from the scope of the invention.

What is claimed is:
 1. A tensioning system comprising: a base; an armpivotally coupled to said base, said arm having an engagement surfaceand being configured to pivot relative to said base about a pivot axis;a biasing mechanism operatively coupled to said arm to bias said armrelative to said base; and a seal assembly sealingly positioned betweensaid arm and said base, wherein said seal assembly is coaxial with saidpivot axis and configured to accommodate relative axial movement betweensaid base and said arm and relative radial movement between said baseand said arm while still maintaining a seal therebetween, wherein saidseal assembly includes a seal body and a deflectable flange coupled toand extending axially away from said seal body, and wherein said flangeis in axial compression.
 2. The system of claim 1 further comprising abushing positioned between said arm and said base, and wherein said sealassembly is positioned and configured to block external contaminantsfrom reaching said bushing.
 3. The system of claim 2 wherein said systemis configured such that sufficient wear in said bushing causes at leastone of relative axial movement between said base and said arm orrelative radial movement between said base and said arm.
 4. The systemof claim 2 wherein said bushing is positioned in a sealed cavity.
 5. Thesystem of claim 1 further comprising a bushing positioned directlyaxially between said arm and said base, and wherein said system isconfigured such that sufficient wear in said bushing causes relativeaxial movement between said base and said arm, and wherein the sealassembly is configured to accommodate relative the axial movementbetween said base and said arm while still maintaining the sealtherebetween.
 6. The system of claim 1 wherein said seal assembly ispositioned radially outside said biasing mechanism and configured toblock external contaminants from reaching said biasing mechanism.
 7. Thesystem of claim 1 wherein said engagement surface is rotatable about anaxis that is radially offset from said pivot axis.
 8. The system ofclaim 1 wherein said seal assembly includes a lip seal, or a X-ring, ora U-ring extending circumferentially about said pivot axis.
 9. Thesystem of claim 1 wherein said seal is in tension in the radialdirection.
 10. The system of claim 1 wherein said seal assembly includesa seal with clearance on both radial sides thereof to enable said sealto move in either radial direction to accommodate said relative radialmovement between said arm and said base.
 11. The system of claim 1wherein said arm includes an outer flange positioned radially outsidesaid base, and wherein said seal assembly includes a seal positionedradially between said flange and said base.
 12. The system of claim 11wherein said arm includes a generally annular plate positioned at anaxial end of said flange and aligned in a radial plane, and wherein saidseal sealingly engages said plate.
 13. The system of claim 11 whereinsaid base includes a radially-outwardly protruding end flange, whereinsaid seal sealingly engages said end flange, and wherein said seal ispositioned between said engagement surface and said end flange in anaxial direction.
 14. The system of claim 11 wherein said seal assemblyis positioned generally at an axial midpoint of said base.
 15. Thesystem of claim 1 wherein said arm includes a portion positionedradially inside at least part of said base, and wherein said sealassembly is entirely positioned radially between said portion and saidbase.
 16. The system of claim 15 wherein said base includes an axiallyprotruding stop, and wherein said seal assembly sealingly engages saidstop.
 17. The system of claim 1 further comprising a cover fixedlycoupled to said base at an axial end thereof, and a supplemental sealassembly sealingly positioned between said arm and said cover.
 18. Thesystem of claim 17 further comprising a bushing positioned between saidarm and said cover, and wherein said supplemental seal assembly ispositioned and configured to block external contaminants from reachingsaid bushing.
 19. The system of claim 17 wherein said cover is a springcap or a deflected arm plate.
 20. The system of claim 1 furthercomprising a bushing positioned between said arm and said base, andwherein said seal assembly is positioned and configured to blockexternal contaminants from reaching a first exposed end of said bushingand wherein the system further includes a supplemental seal assemblypositioned and configured to block external contaminants from reaching asecond, opposite exposed end of said bushing.
 21. The system of claim 20wherein said system is configured such that sufficient wear in saidbushing causes relative axial movement between said base and said arm,wherein said relative axial movement causes one of said seal assembliesto compress and the other one of said seal assemblies to expand.
 22. Thesystem of claim 1 further comprising a power transmitting element in theform of an endless loop, and wherein said engagement surface engagessaid power transmitting element as biased by said biasing mechanism toapply force to said power transmitting element and induce tensiontherein.
 23. The system of claim 1 wherein said seal assembly includes acentral axis which is aligned with said pivot axis.
 24. The system ofclaim 1 wherein said seal assembly is configured to accommodate relativemovement between said base and said arm axially away from each otherwhile still maintaining a seal therebetween.
 25. The system of claim 1wherein said seal assembly is configured to accommodate relative axialmovement between said base and said arm in a first direction axiallyaway from each other while still maintaining a seal therebetween andwherein said seal assembly is configured to accommodate relative axialmovement between said base and said arm in a second, opposite directionaxially toward each other while still maintaining a seal therebetween.26. The system of claim 1 further comprising a bushing positionedbetween said arm and said base, and wherein said bushing is positionedradially outside said biasing mechanism.
 27. The system of claim 1wherein said arm includes a seal counterface aligned in a radial plane,and wherein said seal sealingly engages said seal counterface.
 28. Thesystem of claim 1 wherein said axial compression constitutes compressionin a direction parallel with said pivot axis.
 29. The system of claim 1wherein said seal assembly includes a seal body and a deflectable flangecoupled to and extending axially away from said seal body, and whereinsaid flange is in axial compression.
 30. The system of claim 29 whereinsaid base includes a surface generally aligned in a radial plane, andwherein said arm includes a surface generally aligned in a radial plane,and wherein said seal assembly engages both of said generallyradially-aligned surfaces and is axially compressed between saidgenerally radially-aligned surfaces.
 31. The system of claim 30 whereinsaid seal body engages said base and said deflectable flange engagessaid arm.
 32. A tensioning system comprising: a base; an arm pivotallycoupled to said base, said arm having an engagement surface; a biasingmechanism operatively coupled to said arm to bias said arm relative tosaid base; a seal assembly sealingly positioned between said arm andsaid base; and a bushing positioned axially between said arm and saidbase, wherein said system is configured such that sufficient wear insaid bushing causes relative axial movement between said base and saidarm, and wherein the seal assembly is configured to accommodate saidrelative axial movement between said base and said arm while stillmaintaining a seal therebetween and wherein said seal assembly includesa seal body and a deflectable flange coupled to and extending axiallyaway from said seal body, and wherein said flange is in axialcompression.
 33. The system of claim 32 wherein said seal assembly isconfigured to accommodate relative movement between said base and saidarm axially away from each other while still maintaining a sealtherebetween.
 34. The system of claim 32 wherein said bushing ispositioned radially outside said biasing mechanism.
 35. A tensioningsystem comprising: a base; an arm pivotally coupled to said base, saidarm having an engagement surface; a biasing mechanism operativelycoupled to said arm to bias said arm relative to said base; a bushingpositioned between said arm and said base and positioned radiallyoutside said biasing mechanism; and a seal assembly sealingly positionedbetween said arm and said base, wherein the seal assembly is configuredto accommodate relative axial movement between said base and said armand relative radial movement between said base and said arm while stillmaintaining a seal therebetween, and wherein said seal assembly ispositioned radially outside said biasing mechanism and configured toblock external contaminants from reaching said biasing mechanism, andwherein said seal assembly includes a seal body and a deflectable flangecoupled to and extending axially away from said seal body, and whereinsaid flange is in axial compression.
 36. The system of claim 35 whereinsaid seal assembly is configured to accommodate relative movementbetween said base and said arm axially away from each other while stillmaintaining a seal therebetween.
 37. The system of claim 35 wherein saidbushing is positioned radially between said arm and said base.